Mucosal biopsies from the alimentary canal from patients infected with Norwalk agent will be studied by immunoelectron microscopy for evidence for viral proliferation. Glycoprotein synthesis and secretion will be studied in cultured rectal biopsies from patients with cystic fibrosis and their asymptomatic first order relatives. Epithelial cell proliferation will be examined by radioautographic methods in the stomach of fetal rodents. The fine structure of fetal rodent and available fetal human small intestine will be examined by electron microscopy. Segments of fetal rodent stomach, small intestine and colon will be maintained in organ culture, and the effect of putative substances that may affect organogenesis will be studied in this system.